This invention relates to a routing control system for use in a radio access network and, in particular, to a routing control system of a dynamic routing type.
A radio access network system is used to connect computers with one another and to transmit packets among the computers. The computers are, for example, personal computers and/or workstations. The radio access network system comprises a plurality of base stations each of that is connectable to one of the computers by radio. The base stations adopt a point-to-point protocol to communicate with the computers respectively. Each of the computers can transmit a packet to any one of the other computers through the radio access network system.
A conventional base station used in the radio access network system includes a router adopting a routing information protocol (RIP) or an open Shortest path first (OSPF) method to control dynamic routing.
The RIP gives the radio access network a shortest path from a source base station to a destination base station. Furthermore, the RIP periodically makes the router exchange routing control information with adjacent routers to update a touring table memorized in the router, thereby the RIP can deals with a fault (such as a cutting) of a link between the base stations and with addition (or attachment) of an additional base station to the radio access network.
However, the RIP has a problem that a hop number is limited to a predetermined number. That is, the RIP can not route a packet when the number of the base stations on the shortest path between the source and the destination base stations is not smaller than the predetermined number.
The OSPF method is suitable for a large-scale network larger than a network such that the RIP is adopted because it does not have the above mentioned limitation of the hop number. In addition, the OSPF method decides a shorter route between the source and the destination base stations after consideration of traffic congestion of the network.
However, the OSPF method is an exaggerated method for the radio access network system such that the base stations are connected to the computers respectively by using the point-to-point protocol.
Additionally, both of the RIP and the OSPF method have a common problem that static routing control is necessary to avoid a state that the packet circulates in a loop included in the radio access network. That is, a network manager of the radio access network must pay attention to loops of the base stations. The problem mars degree of freedom regarding attaching/removing base station to/from the radio access network.